1. Scope of Invention
This invention relates to an anchorless boat positioning system and more particularly to a multi-mode system for accurately approaching and maintaining a pre-selected location of a floating vessel without the use of a physical anchor.
2. Prior Art
Boat anchors have been used for thousands of years. The anchor is attached to the boat with a line or xe2x80x9crodexe2x80x9d and then lowered overboard so that the flukes and/or shear weight of the anchor dig into the water bottom. Problems exist, however, in using anchors in certain settings. The depth of the water may prohibit anchoring because the length of the line needed to reach the water bottom with proper scope is impractical.
Moreover, even if the anchor reaches the water bottom, the depth of the water may be so great that it becomes difficult to maintain the anchored boat within close proximity to a desired position when varying wind or water currents are present. The line from the boat to the anchor acts as a tether allowing the boat, subject to the current and wind, to swing about an arc whose radius is nearly that of the length of the anchor line.
In small watercraft, manually lowering and raising a conventional anchor is also strenuous and time consuming, plus there is always the possibility of the anchor becoming fouled on the bottom, a common aggravation for the skipper.
Further, the use of anchors may be restricted in waters where, for example, underwater cabling has been installed (usually indicated on navigational charts) or where a salvage operation is taking place. The use of anchors which dig and plow has also come under criticism for causing severe damage to fragile underwater ecosystems. For example, anchors of fishing vessels have caused significant damage to long-standing coral reefs, resulting in these areas being designated as xe2x80x9cNo Anchoringxe2x80x9d areas.
In U.S. Pat. No. 5,386,368, Knight teaches an apparatus for maintaining a floating boat or water vessel in a desired position. The apparatus includes an electric trolling motor disposed to produce a thrust to pull the boat, a steering motor disposed to affect the orientation of the electric trolling motor, a position deviation detection unit and a control circuit. The position deviation detection unit detects a deviation in the position of the boat from the desired position and transmits signals indicative of a deviation distance and a return heading to the control circuit. The control circuit causes the steering motor to steer the electric trolling motor in the return heading, and the electric trolling motor to propel the boat in the return heading to return the boat to the desired position. A first embodiment of the position deviation detection unit detects a deviation in position based on signals from a satellite-based global positions system. Another embodiment detects a deviation in position based on a signal from an anchored transmitter. A third embodiment detects a deviation in position based on the forces caused by the surrounding water when the boat drifts.
As disclosed in U.S. Pat. No. 5,491,636 by Robertson, et al, the invention allows a boat to be dynamically and automatically held in position at a selected anchoring location on the water without the use of a conventional anchor line, or winch by controlling the thrust and steering of a thruster (e.g., trolling motor) attached to the boat. The thruster is controlled on the basis of signals received from global positioning system (GPS) satellites orbiting the earth and a digital magnetic compass mounted on the thruster. The signals from the GPS satellites provide an ongoing indication of the position of the boat in earth positional coordinates while the compass provides continuous heading indications of the thruster. With this information, a controller compares the positional coordinates of the selected anchoring location with the positional coordinates of the boat""s current location and generates steering and thrust signals to the thruster to move the boat to the anchoring site.
The global positioning system (GPS), available for use by both civilians and the military, is a multiple-satellite based radio positioning system, placed into orbit by The United States of America Department of Defense, in which each GPS satellite transmits data that allows a user to precisely measure the distance from selected ones of the GPS satellites to his antenna and to thereafter compute position, velocity, and time parameters to a high degree of accuracy, using known triangulation techniques. The signals provided by the GPS can be received worldwide twenty-four hours a day. The accuracy in determining the earth positional coordinates may be augmented through the use of a differential reference station for providing differential correction information (DGPS mode) to the receiver.
In one general aspect of the ""636 patent, an anchorless boat positioning system for substantially maintaining the position of a boat at a desired location includes one or more thrusters attached to the boat for moving the boat to the selected location within the water, a GPS receiver receiving signals from GPS satellites for providing position information signals indicative of the position, of the boat, a magnetic compass for providing a heading indication signal representative of the direction the thruster is pointed, and a controller (e.g., computer) for providing control signals to control the magnitude and direction of the thrust on the basis of the position information signals from the GPS receiver and the heading indication signal from the magnetic compass.
Embodiments of the ""636 patent included one or more of the following features. The control signals are based on the range, rate of change in range, and bearing from the present location of the boat to the selected anchoring location. A single thruster, fully rotatable about a vertical axis extending from above the surface of the water to below the surface of the water and transverse to the direction of propulsion of the thruster, is used to maintain the position of the boat. The control signals include thrust control signals for varying the amount of thrust generated by the thruster and steering control signals for controlling the direction that the thruster is pointing. The thruster is typically attached to the bow of the boat. The anchorless positioning system may include a GPS reference receiver positioned at a known location different from the position of the GPS receiver aboard the boat with the GPS receiver on board the boat receiving signals from both the GPS reference receiver and the GPS satellites to provide position information signals differential GPS mode, a technique for improving the accuracy in determining earth positional coordinates. The magnetic compass provides a heading indication signal representative of the heading of the thruster. The control signals relate to the difference between a present position and a selected location.
Optionally, a first non-rotatable thruster was used for providing thrust in a direction along a long axis of the boat and a second non-rotatable thruster for providing thrust in a direction transverse to that of the first non-rotatable thruster to maintain the heading of the boat toward the selected anchor location. The controller provides thrust control signals to the first non-rotatable thruster and steering control signals to the second non-rotatable thruster. An additional thruster may be positioned at the stern of the boat to assist in propelling the boat in the direction of the boat""s heading.
In another aspect of the ""636 patent, a method of substantially maintaining a position of a boat at a selected location in water included receiving and storing position information signals from GPS satellites with a GPS receiver to establish positional coordinates of a selected anchoring location: receiving, after a predetermined period of time, position information signals from the GPS satellites with the GPS receiver to determine a present location of the boat and a present heading indication of the thruster from the magnetic compass; and controlling the magnitude and direction of the thrust of at least one thruster on the basis of the difference between the positional coordinates of the anchoring location and the present location.
This invention is directed to an anchorless boat or water vessel positioning system for maintaining a boat at a selected anchoring location within water without the use of a conventional anchor. A steerable thruster is used whose thrust and steering direction are determined and controlled on the basis of position information signals received from global positioning system (GPS) satellites and heading indication signals from a magnetic compass. The anchorless positioning system continuously monitors the position and heading of the boat and compares it with the stored coordinates of the selected anchoring location(s) to generate control signals for the steerable motor. Several modes of operation are disclosed and Euler transformations for offset antenna placement for error reduction are taught. Proportional, integral, and derivative control (PID) of three constants of vessel control is also provided.
It is therefore an object of this invention to provide a boat positioning and anchoring system which will accurately position and hold a floating vessel on a body of water in a preselected point on the water aided by GPS data.
It is yet another object of this invention to provide a multi-operational mode virtual anchor system which may also be used in trolling-type fishing and under manual operation through the use of a remote hand-held controller.
Still another object of this invention is to provide a boat positioning and anchoring system which operates under proportional, integral and derivative (PID) control for superior performance and capability in achieving and maintaining a desired anchor point of a floating vessel.
Yet another object of this boat positioning and anchoring system is to accommodate GPS antenna placement remote from the rotational axis of the thruster both horizontally and vertically.
In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with reference to the accompanying drawings.